Humans, livestock and rat monocrotaline (MCT) pneumotoxicity is associated with a spectrum of pulmonary vascular lesions reminescent of idiopathic pulmonary hypertension in humans. Studies in our laboratories demonstrates that the polyamines have a central role in the MCT-caused pathogenic vascular structural remodeling. Research proposed herein explores molecular and biochemical mechanisms through which polyamines comprise an obligatory link between the initial hypertensive stimuli and the vascular thickening. To test the hypothesis that polyamines mediate MCT-induced endothelial dysfuntion, (1) autoradiograph and immunocytochemistry will be used to determine if endothelial cells in the lungs of MCT-treated rats exhibit a temporally enhanced ODC activity related to perivascular edema formation; (2) Cultured endothelial cells will be used to determine if MCT- derived pyrroles directly provoke polyamine dependent endothelial injury; and (3) Perfused lungs isolated from MCT-treated rats will be used to determine if MCT-induced depression of endothelial serotonin uptake is polyamine-dependent. To assess mechanisms by which polyamines mediate MCT-induced hypertensive pulmonary vascular remodeling, autoradiograph and immunocytochemistry will be used to determine; (5) if MCT enhances polyamine biosynthetic activity in specific vascular cells that are functionally related to vascular remodeling; and (6) if DNA and protein synthesis are activated in the same cell types in which polyamine biosynthesis is enhanced. (7) In vitro hybridization will be employed to determine ODC and Collagen gene(s) expression and modulation at the individual cell level; (8) cultured cells and isolated pulmonary arteries will be used to determine if enhanced collagen gene expression is regulated by altered ODC gene expression; (9) Molecular mechanisms by which MCT alters ODC gene expression will be explored. Potentially clinically relevant studies will determine (10) if MCT pneumotoxicity can be reversed by polyamine biosynthesis inhibition. Rats exposed to chronic hypoxia (an established pulmonary hypertension model) will be studied to: (11) characterize the time-dependent effects of hypoxic exposure on lung polyamine biosynthesis, (12) determine if polyamine biosynthesis inhibition forestalls hypoxic pneumotoxicity, and (13) immunocytochemically identify lung cell types in which chronic hypoxia enhances ODC content.